Spindles isolated from eggs of marine animals can be treated with calcium or cold and will lose their birefringence and corresponding microtubules. Nevertheless the structure which is left, the remnant, is spindle shaped and contains the chromosomes in metaphase or anaphase configuration. Eggs with spindles may be treated with nocodazole or cold for several minutes prior to spindle isolation in which case on non-birefringent structure greatly resembling the spindle remnant is isolated. These observations strongly suggest that the spindle remnant is a preexisting structure which acts as the matrix within which microtubules form and function. We will study this structure both morphologically and biochemically emphasizing a set of proteins which we find in both clam and sea urchin spindles. These are proteins which react with anti-mammalian vimentin and a 55 KD protein (a doublet in clam eggs) which behaves in extraction like an intermediate filament protein but which does not react with antibodies to such proteins. In addition, we will examine the different localizations of microtubule associated proteins (MAPs) which are defined by ability to cycle with tubulin compared to ability to attach to microtubules during taxol polymerization. Finally, we will use tubulin, MAPs and remnants to investigate incorporation of tubulin into the spindle matrix in vitro and will utilize these components, various spindle polymerization media and egg extracts to reconstruct chromosome motion in vitro.